Apoptosis, programmed cell death, is a normal physiological phenomenon which can be observed in various tissues. Since deregulation of apoptosis can contribute to tumorigenesis, elucidation of nutritional modulation of the apoptotic pathways will contribute to cancer prevention and therapeutic strategies. Thus, our goals are 1) to identify nutritional and dietary factor(s) which modulate the apoptotic pathways and 2) to investigate the mechanisms underlying this modulation. The protein Bcl- 2 has been shown to be a component of the apoptotic pathway. Overproduction of Bcl-2 protein resulted in blockage of apoptosis and increased survival upon external "death" stimuli. The anti-apoptotic activity of Bcl-2 is thought to be modulated by the protein Bax, and it has been proposed that the ratio of Bcl-2 to Bax protein may determine whether a cell would undergo apoptosis. Breast epithelium undergoes cyclic apoptosis and fluctuation in Bcl-2 protein level during the menstrual cycle. Clinical studies showed a relationship between estrogen receptor (ER) expression and Bcl-2 protein level. Thus, steroid sex hormones such as estrogen may regulate Bcl-2, Bax levels, and consequently apoptosis. Exposure to estrogen has been associated with increased incidence of breast cancer, hence, better understanding of its role in apoptosis could be important in prevention and treatment of breast cancer. We utilized estrogen receptor positive human breast cancer MCF-7 cells as a model to address two questions: 1) Is Bcl-2 and Bax mRNA expression regulated estrogen? 2) Does estrogen regulate apoptosis? We developed a reverse transcription-polymerase chain reaction method to quantitate the expression of mRNA for Bcl-2 and Bax, two modulatory proteins in the apoptotic pathway, in human breast cancer cell line MCF- 7. We found that the Bcl-2 mRNA levels in the cells exposed to 17 beta-estradiol was higher than that of control cells, while the relative Bax mRNA levels remained unchanged. The changes in Bcl-2 mRNA level occurred in a time and concentration-dependent fashion. In addition, pretreatment with 17 beta-estradiol protected MCF-7 cells from apoptosis. Our study provides evidence that responses of breast epithelial cells toward a steroid sex hormone involves regulation of the apoptotic pathway. We are currently investigating modulation of this pathway of dietary factors.